1. Field of the Invention
The present invention relates to a novel flame resistant resin composition comprising an epoxy resin and a halogenated polyhydroxystyrene and further a novel metal clad laminate prepared using the above-described flame resistant thermosetting resin composition.
2. Description of the Prior Art
Hitherto, as flame retardants for epoxy resins and other resins, addition-type flame retardants such as low molecular weight halides, antimony trioxide, and phosphorus compounds are generally used but since these addition-type flame retardants not only adversely influence the properties of the resins to which the flame retardants are added but also recently have caused large problems due to their toxicity, reactive type flame retardants or further flame retarding high molecular weight compounds have tended to be employed in place of these addition-type flame retardants. That is, by employing high molecular weight flame retardants in place of low molecular weight flame retardants, the properties of the resins containing the flame retardants can be improved and stabilized and also the adverse influences on humans can be greatly reduced, that is, such high molecular flame retardants are not toxic to humans.
From such a standpoint, investigations on the development of flame retarding epoxy-phenol type thermosetting resins based on the fact that a halogenated polyhydroxystyrene is not only a reactive type resin but also simultaneously a high molecular type resin and as the result of these investigations it has been found that the flame resistance of the epoxy-phenol type resins as previously provided by Japanese Patent Application No. 109,675/'72 can be further improved by using the above-described halogenated polyhydroxystyrene.
Furthermore, with the recent rapid development of the electronic industry, a metal clad laminate for printing circuit use has become an important component of electronic equipment. Hitherto, most metal clad laminates are those composed of papers and phenol resins produced by high pressure molding but these paper-phenol resin type metal clad laminates have the disadvantages that their electric properties vary greatly depending on changes in temperature and humidity, they are deformed greatly by heat or by changes in humidity, which causes operational difficulties due to imperfect contact, and further they lack sufficient thermal stability for soldering and sufficient chemical resistance. Accordingly, it becomes difficult to provide the required properties increasingly rapidly demanded in the fields of household appliances, industry, and communications. Thus, the demand for epoxy resin metal clad laminates employing glass cloths or glass mats as the base material which do not have these disadvantages has recently greatly increased and further it has keenly been desired that metal clad laminates have not only improved thermal stability at soldering but also excellent flame resistance so that the efficiency of the soldering operation could be improved and also so that safety and reliability could be improved.
It has also been further confirmed that a flame retarding composition comprising an epoxy resin and a halogenated polyhydroxystyrene has also excellent electrical properties and high reliability as commercial products. Thus, on considering the above-described recent situations on metal clad laminates, the possibility of the application of the above-described flame retarding composition for the metal clad laminates has been further investigated for meeting the increasing requirements of the properties of metal clad laminates, in particular, high thermal stability at soldering, high flame resistance and high reliability as commercial products, and as the result of these investigations metal clad laminates having excellent thermal stability and flame resistance as well as high reliability have been successfully obtained by using a material impregnated with the flame retarding resin composition as a base material for metal clad laminates.